Abstract 1697: Role of the Posterior Left Atrial Septo-Pulmonary Bundle in Wavebreak Formation During Atrial Fibrillation by Pulmonary Veins Impulses
It is well known that foci in the pulmonary veins (PVs) act as triggers and the posterior left atrium (PLA) is a substrate for atrial fibrillation (AF). However, the role played by the complex anatomical structure of the PLA in AF initiation and maintenance is poorly understood. We hypothesized that burst pacing of a PV would yield wavebreaks (WBs) in PLA areas of both changing fiber direction and increased wall thickness. In 8 Langendorff-perfused sheep hearts, we exposed the septal and PLA endocardial surfaces to obtain high resolution optical maps (DI-4-ANEPPS, 1000-fr/s, 5 sec movies) of AF elicited by a burst of 6 PV pulses (5 ms duration; 80–150 ms) triggered by the sinus impulse. Phase movies allowed visualization of WBs. PLA wall thickness was measured by echocardiography. In separate sheep, we determined fiber direction at the PLA after pealing of endocardium (binocular dissecting microscope, Watchmaker’s forceps). In 13 episodes we compared the location of WBs at AF onset vs 2–5 minutes of stable AF (Figure⇓). Regardless of whether burst stimuli emerged from the right or left PVs, at AF onset the WBs (dots) preferentially located near the PLA-septal junction. WBs were randomly distributed after 2–5 minutes of stable AF. The PLA-septal junction was significantly thicker than the rest of the PLA (0.71±0.1 vs 1.4±0.04 cm, p=0.003, ANOVA), demonstrated sharp changes in fiber direction at a specific septo-pulmonary bundle crossing the PLA, and showed delayed conduction. We conclude that during AF initiation WBs preferentially occur near the PLA-septum junction at the septopulmonary bundle constituting an area of increased myocardial thickness and abrupt change in fiber direction.